The invention relates to an electric input key having an actuating surface.
Such input keys are used, for example in motor vehicles, to input switching desires in shift-by-wire switching actuation systems. The displacement sensor system of the input key can be redundantly designed by using a plurality of digital sensors, for example microswitches.
DE 10 2008 015 910 A1 discloses an electric input key, the actuation of which causes a plurality of switches to switch at the same time. A possible malfunction can be determined using a diagnostic routine. For this purpose, a test signal is generated, which test signal is applied to one or more switches and is evaluated by a control unit.
Electric input keys having digital displacement sensors, in which three digital switches are used for example, are also known. A particular switching state or a state change is detected by the signal from two of the three digital switches, with the result that the malfunction of an individual digital switch has no effects. However, such conventional electric input keys having a plurality of redundant digital displacement sensors also have disadvantages. On account of unavoidable mechanical tolerances, the displacement sensors installed in an input key or a switching input unit have different switching points. If the input key or another input element is actuated only to the extent that not all displacement sensors switch, the displacement sensor which has not yet switched is incorrectly diagnosed as defective. Over the service life, wear of the mechanical components may result in shifts of the switching points of the displacement sensors, which shifts may result in an increase in the switching point differences between the individual sensors. This may result in an increase in the above-described false diagnoses of individual displacement sensors.